Gamma correction for blending 2 projector-images

    May 16 2006 | 1:33 pm
    Hi there,
    for a rather simple 2-projector video installation, I wrote a patch to blend the edges. Up to now just by using a grayscale matrix for the alpha channel that I send to an
    Now, what's the actual problem: I am worried, that I will need some gamma correction in the blending area as up to now I am just adding pixel values in this area. Does anyone have some experiences with edge blending (because I don't) in Jitter and how to do the gamma correction best? I know about the jit.displays abilities and was thinking about using the "coords"-message to define the area of gamma adjustment. I won't be able to try around much with the two projectors running, so I have to prepare everything beforehand and want to get sure that I am on the right track - so thanks a lot for any advice.

    • May 18 2006 | 10:43 am
      come om guys,
      there should be somebody with some experiences in edge-blending.
    • May 18 2006 | 2:37 pm
      never done the edge blend, but don't think you can selectively adjust the gamma for only a portion of the display - it's all or nothin. You can adjust the gradient that you are using for the alpha channel using jit.charmap....
    • May 18 2006 | 2:48 pm
      hi tom
      don't know about your budget but there are projectors wich are able to do this for you
    • May 18 2006 | 6:42 pm
      Note that in addition to modifying the gamma table of the display device, you can also use jit.charmap to apply any kind of transfer curve to either your color data or your alpha data necessary. Simply fill your transfer curve look up table with the appropriate entries. For gamma adjustment it would be something like output_value = pow (input_value,gamma), where input/output values are (0.-1.). You'll of course need to convert to/from the range (0-255) for your lookup table. That formula is a simpliication of the standard gamma equation which might be satisfactory for your purposes, but here's some more info with more detailed description of how gamma is typically calculated.
      Hope this helps.